A member of the team that just discovered the tau neutrino talks about the lure of tiny particles that no one can see and few can understand. By GEORGE JOHNSON

Photograph by Tom Maday

Three weeks ago, you and a team at Fermilab finally found the long-sought particle called the tau neutrino. An old French mathematician once said that a theory is not complete until you can explain it to the first person you meet on the street. Why is finding the particle so important?

In a really broad sense, it's a confirmation that the universe is understandable. From a less metaphysical standpoint, it's a confirmation that the 12th particle that makes up the universe -- the tau neutrino -- does exist. My image is the construction of an arch. The arch is supported by all of its constituents, and it takes a keystone to ensure its stability. The keystone is the last piece to go in.

Time after time, theorists invent a particle they need for a pet theory to work and -- voila! -- experimenters go and find it. Do you find that a little eerie?

Comforting, I would say. If somebody says, "Hey, we can't find the particle," then either the experiment is wrong or the theory is wrong. That's the fun. Everybody likes a good mystery.

In the experiment, you used enormously high energies to smash protons, sparking off tau neutrinos and a whole mess of other things. It sounds so dramatic -- as though scientists were gathered around a huge Frankensteinian console when suddenly an alarm goes off and an unsuspecting tau neutrino is found writhing in the net. Surely the climax is, in reality, far more drawn out?

Yes, yes. There is a line I remember from a novel, "I'm a disciple of delayed gratification." You don't want to get too excited. Unless you've looked at every aspect and understood all the possibilities, you could just be fooling yourself. It happens so many times in science that it's something to guard against religiously.

With no charge and only the tiniest mass, neutrinos sometimes seem more like wisps of mathematics than real things. Are they maddeningly hard to catch?

Yes. When you're sitting there in the control room at 3 o'clock in the morning, you don't have any instant feedback telling you that you've done things right. All you're left with in the end is this exposed emulsion and a bunch of computer tapes. It may take you a few months before you can convince yourself that you've actually seen neutrino interactions. There's always this worry that you've spent all this money and invested all this time and there is something you've overlooked -- and it's too late to do anything about it.

When you're in the midst of one of these experiments, it must be like living in a different world.

Well, it's a pleasant world, even though it has this nerve-racking quality to it. After all the planning, the reviews, the lobbying for funding, and all the administrative things, finally, the experiment is running. And it's pleasantly dull.

Do you ever feel a sense of total immersion?

Yeah, in particular when you're working the owl shift in this control room. Your major interactions are either with the people who might be on shift with you or the operators in the accelerator, and then you go home and sleep and the regular life of the laboratory proceeds.

Is it ever alienating?

It can be, yes, to finally go back to work and realize that people eat lunch at noon and things like that.

It must be hard to explain your work at a dinner party.

Yeah, the eyes glaze over rather rapidly when I start talking about things like neutrino oscillations. Many people have heard these terms and expect that it might take two or three minutes to explain everything they need to know. They'll say, "Aha, I understand that." But after those two or three minutes are over, they start to lose interest.

Some experimenters complain that the theorists, with their cosmic speculations, get all the glory. Why did you choose to work in the trenches?

There is a simple answer: I'm not smart enough to be a theoretical physicist. I started out in mechanical engineering and decided that physics, in the long run, is more satisfying. You're figuring out how the world works. And I've always been mechanically inclined. Experimental physicists get their hands dirty. They have the enjoyment of going out and putting electronic circuit boards together. A place like Fermilab is sort of like a toy shop. You get to play with the toys.